DESCRIPTION (provided by investigator): Attention Deficit Hyperactivity Disorder is amongst the most commonly diagnosed mental health disorders. Recent estimates suggest that it affects 2-4% of adults, with consequences that include life histories of academic and occupational failure, interpersonal difficulties and stimulus seeking behaviors. One key challenge for developing our scientific understanding of ADHD is a paucity of objective measures of symptom severity. Such measures would provide valuable tools for basic research programs that call for continuous and quantitative measurements of the core deficits in ADHD subjects (endophenotypes) by allowing measurements of more subtle influences of disease precursors (e.g., genetic or environmental factors) than is possible with symptom checklists. We propose to investigate a psychophysical procedure for estimating an individual's ability to resolve visaul interference. Our preliminary data reveal that ADHD subjects have a severe deficit in discriminating targets in high interference displays, even though they show normal performance with equally challenging displays that do not contain distracting stimuli. These data suggest that ADHD subjects have a strong and selective deficit in the resolution of perceptual interference. We propose a comprehensive assessment of the integrity of visual interference resolution in well characterized ADHD and control popultions, with sample sizes large enough for a careful examination of the influence of co-morbid disorders and ADHD subtypes. In addition, we will use procedures developed within our lab that enable a selective manipulation of the degree to which interference is resolved at attended locations. These tasks, in conjunction with fMRI and event-related electrical recordings of the brain, will provide an in-depth analysis of the behavioral and neural characteristics for interference resolution in ADHD subjects, which may help to identify the underlying cognitive impairments that cause the severe disruptions in resolving interference in this population. Finally, given that most theories of ADHD suggest a modality independent deficit in attentional functions, we will examine whether ADHD subjects have similar difficulties with the resolution of interference in the auditory domain. Our initial studies will focus on the basic question of which dimensions within auditory perceptual space (i.e., spatial, temporal or spectral) provide the best analog to the spatial dimension that determines interference in the visual domain.